This invention relates to superconductive metal oxide ceramics, in particular to Bi.sub.2 Sr.sub.2 CaCu.sub.2 O.sub.8 (Bi(2212)) and Bi.sub.2 Sr.sub.2 Ca.sub.2 Cu.sub.2 O.sub.3 (Bi(2223)), and may be applicable to lead doped Bi(2212) and Bi(2213).
The technology of superconductivity, particularly metal oxide ceramics which conduct electricity with no resistance at temperatures above the boiling point of liquid nitrogen, unlike previously known materials that can superconduct only near absolute zero, has been rapidly developing. These materials, i.e. certain metal oxide ceramics, can conduct electricity with no resistance at temperatures above the boiling point of liquid nitrogen (77K or -196.degree. C.). The discovery of these materials has been quite recent and the demand for practical application of these materials will be ever increasing in the future. In particular, it is desirable to develop these new metal oxide ceramics, particularly Bi(2212) and Bi(2223) and lead doped varients thereof into useful conductor shapes such as wires, films, or thin sheets.
An enormous amount of effort is being devoted to exploring ways of making wire out of the new high temperature superconductors. In many applications a composite multi-filamentary wire will be required. Such wire cannot be made by drawing rods into filaments because of the extreme brittleness of the new materials.
Accordingly, there is a continuing need for alternative methods of making filaments of the high temperature superconductors of Bismuth such as these here described. This invention has as its primary objective the fulfilling of this need.
The conditions under which the ceramic is prepared affect the superconductivity. This is important because the fibers as initially prepared are not superconducting and must be made superconducting with a heat treatment. This invention is particularly useful in making Bi(2212) and lead doped varients thereof, but may also be applied to Bi(2223).
A primary objective of this invention is to use the pendant drop melt extraction technique to produce superconductor fibers in a manner in which the superconductivity is not permanently destroyed by the process of pendant drop melt extraction. This has heretofore not been achievable, primarily because the conditions normally utilized for pendant drop melt extraction affect ceramic as well as the formation of new phases and may destroy superconductivity. In this process superconducting can be restored after pendant drop melt extraction by a simple heat treatment.